What controls needed for running two boilers in parallel?
Phil Addison
boiler periodically cutting out". The decision has now been made to
replace it, and the recommendation we have, which I think is reasonable,
is to replace the ancient 41kW beastie with a pair of 24kW
Worcester-Bosch system boilers (model 24i) running in parallel.
This existing system is sealed, and the Chaffoteaux has an internal pump
circulating primary water through a low-loss header* (LLH), and there is
a separate pump circulating the LLH contents around the radiators which
are spread over 4 floors, see ASCII art below. This is heating only, no
domestic hot water.
Currently one radiator is open valved and the others have TRVs.
The proposal is that the two new boilers will each have their own pump
and check valve, and that combination will be connected in parallel and
tee'd into the existing low-loss header. A magnetic strainer will be
included.
So far that seems straightforward. My concern is the control system to
ensure the pair of boilers work at maximum efficiency. When it is mild
we want one boiler only to be running, and the second cutting in only
when more that 24kW is required. Clearly one boiler running at full
power will be much more efficient than two running at half power. and
for most of the year we should see the benefit of full condensing
operation of one boiler with the other hardly ever firing.
First question is, is there a standard 'box of tricks' that does this? I
have asked W-B who insist they "don't do system design just make
boilers" and could offer no help.
It shouldn't be too difficult to make a controller to do this... my
early thoughts are that starting from a cold system, I want to stop #2
boiler from firing for say 1/2 hour to establish if #1 is coping or not.
That can be decided by checking the temperature rise across the boiler;
once its stabilized (after the 1/2 hr) I can say that if it is greater
that the spec figure of (say) 11 degrees then it is dumping its full
24kW into the system and #2 needs to be turned on to supplement it.
So far so good, but with two boilers now running, how do I control
things so that #1 stays at full power and #2 modulates as required until
conditions require #2 to be turned off entirely and then #1 modulates
down. I can see there is scope for instability and hunting here if I'm
not careful.
I'm sure this has all been done before but not sure where to start
looking, having no experience of industrial systems.
Any clues please?
*Chaffoteaux refer to the LLH as a "monotube", which appears to be
simply a 600mm length of 54mm tube with the boiler flow and return teed
in near each end, and the radiator system connected at each end with
28/54mm reducers as below.
[Fixed font ASCII art]
To Boiler
|| ||
(P) ||
__||________||__
====________________====
|| 54mm ||
|| || 28mm
|| (P )
|| ||
To Radiators
Phil
BigWallop
"Phil Addison" <phi...@bigNOSPAMfoot.com> wrote in message
news:41k6i453g7lscslvf...@4ax.com...
Any system I've seen with parallel boilers has been controlled by just one
timer like any other standard system. Both boilers just heat the water when
demanded and the thermostats Etc control the pump and zone isolators and
things, like normal systems do.
If one boiler needs to replenish the heating, it does. If you don't need
two boilers during the warmer months, turn the thermostat right down on one
of them.
Not being familiar with the boiler model, I should ask if they have their
own internal pumps Etc? If the system is to be controlled by an external
pump, then the boilers can be connected in parallel to the feed and return
for the original heating circuit. One external pump will push water through
both boilers like it would with just one.
One fill loop is also enough to flood the closed heating circuit and both
boilers just the same as filling a system with one boiler. There should be
no differences between a system with parallel boilers or just one.
Having two boilers which can supply separate demands to two separate
domestic hot water taps might be a great thing. The bathroom can be
supplied from one boiler, and kitchen utility room from the other.
But I don't see any problem or major control system changes that you will
need. But then again, someone will probably be along in a minute to tell me
I've shot myself in the foot again.
Tony Bryer
> First question is, is there a standard 'box of tricks' that
> does this? I have asked W-B who insist they "don't do system
> design just make boilers" and could offer no help.
The boxes that do this are called sequencers and don't come
cheap.
I had to do this when I replaced our church boiler with a pair of
Kestons back in 2001 and needed a budget solution. What we ended
up with is this:
The ordinary controller goes into the common of a two-way switch
(select lead boiler) with L1 and L2 going to the call for heat on
each boiler. Between L1 and L2 there is a connection which goes
through a room stat (a CM67 on our system) set 1/2 degree or so
lower than the main one, and a pipe stat (normally closed, but
set to open at about 60C) on the return from the heating.
So from cold, both these stats are closed so L1 and L2 are
connected and both boilers run. If the desired temperature is all
but there, the second boiler drops out, and this also happens if
the return temp reaches 60 (i.e the rads are not getting rid of
the heat fast enough).
I did try one or two other refinements but took them out so as
not to make things too complicated for my successor. One was to
use an extra stat to delay pulling in the second one until the
first boiler was fully up to temp (which it never gets to in the
mild spring/autumn days), but without adding yet more
complication this then means that if the first boiler fails, the
second doesn't either, and one of the reasons for having a
2-boiler system is the backup.
In terms of a simple solution, what I really needed (Andrew could
no doubt have designed something), was a delay controller that
would close a relay (say) 15 minutes after power was supplied, so
that in spring/autumn when the boiler was being cycled it never
closed, and if the lead boiler failed the second one was pulled
in after a short delay.
--
Tony Bryer, 'Software to build on' from Greentram
www.superbeam.co.uk www.superbeam.com www.greentram.com
David Hansen
<phi...@bigNOSPAMfoot.com> wrote this:-
>First question is, is there a standard 'box of tricks' that does this? I
>have asked W-B who insist they "don't do system design just make
>boilers" and could offer no help.
As has been said you need a sequencer. Search engines will pull up a
whole variety from bare boards to finished products in enclosures.
One example of the former is
<http://www.intelligentheatingcontrol.co.uk/026.html>
Such a gadget will allow you to set which boiler leads. That can be
done with a switch and thermostats, but an electronic version allows
for things like automatically changing which boiler leads. It may
offer other features like weather compensation.
--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54
YAPH
> Thanks for the earlier advice on subject "Chaffoteaux FlexiFlame 140
> boiler periodically cutting out". The decision has now been made to
> replace it, and the recommendation we have, which I think is reasonable,
> is to replace the ancient 41kW beastie with a pair of 24kW
> Worcester-Bosch system boilers (model 24i) running in parallel.
Not answering your question, I know, but my supplier charges more for the
24i system boiler than the equivalent combi (24i Junior). So if you've got
a use for instantaneous hot water (times two) from your setup you could
have it effectively free.
--
John Stumbles -- http://yaph.co.uk
Life is nature's way of keeping meat fresh
Andrew Gabriel
Kestons very handily (and as far as I know, uniquely in domestic
boiler sizes) have a lockout output signal, so providing the failure
is of a type which generates a lockout, you could use this to
effectively switch the lead boiler. Of course, something like a
failed mains supply won't generate lockout, but you could also
generate your own lockout signal based on loss of supply. This
is exactly what I do with my system -- lockout, or failure of
the boiler supply, triggers an input to my house alarm, which
will then phone me up and tell me the boiler's failed. That still
doesn't cover quite all failures modes. I've had the condensate
trap block and the combustion chamber start filling with
condensate. It still ran for a few hours with almost no heat
output, before the condensate blocked off the flue outlet enough
to go into lockout, and the alarm call me up.
To be honest, the simplicity of your system would be hard to beat.
As control systems get more complex, they normally get less
relible and also more subject to design oversights, and it's not
clear to me that any further gain you could make would be balanced
by the inevitable risk of increased complexity.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
YAPH
> Such a gadget will allow you to set which boiler leads. That can be
> done with a switch and thermostats, but an electronic version allows
> for things like automatically changing which boiler leads.
Thought for the day: if you managed to even out the wear and tear between
the boilers perfectly then you'd get the closest possible to them failing
through wear and tear at the same time :-)
--
John Stumbles -- http://yaph.co.uk
The astronomer married a star
Tony Bryer
> As has been said you need a sequencer. Search engines will
> pull up a whole variety from bare boards to finished products
> in enclosures. One example of the former is
> <http://www.intelligentheatingcontrol.co.uk/026.html>
>
> Such a gadget will allow you to set which boiler leads. That
> can be done with a switch and thermostats, but an electronic
> version allows for things like automatically changing which
> boiler leads. It may offer other features like weather
> compensation.
If you read the tech sheet on this particular unit, the
switching in or out of the second boiler is done by a pipe stat
on the return as per my DIY system. The only refinement is that
the lead boiler is automatically alternated every six hours -
as already pointed out, taken to its logical conclusion this
would lead to both boilers expiring together.
Doctor Drivel
"Phil Addison" <phi...@bigNOSPAMfoot.com> wrote in message
news:41k6i453g7lscslvf...@4ax.com...
Buy a Broag Boiler (Dutch). They are top quality (better than Vaillant) and
are now freely available...and cheaper too, as they are making headway into
the UK market. Their boiler control systems are Opentherm and quite
advanced. They are the best buy by far of any boiler at the mo'. They are
well established in the UK under Remeha, doing excellent commercial stuff
and decided to import their domestic Broag Avantaplus range.
http://www.avantaplus.com/
I don't know what your DHW requirements are. But a good option is use two
24kW combis and split the DHW outputs across the DHW taps - divide and rule.
Combine the outlets using two check valves and a shock arrestor to fill a
bath at over 20 litres/min.
To do the sequencing of the two boilers try these below, which are cheap and
OK. You will have to put the controls into a plastic control box.
The 0-10v output of the weather compensator will input into the boiler
sequencer, thus making one control unit. The boilers will be basic units
with no external controls on them, only being controlled by the weather
compensator via the sequencer.
The weather compensator lowers the flow temperature of the boilers to
promote condensing efficiency and the sequencer decides if one or two
boilers needs to be brought in. Also, boiler cycling is at a minium.
Boiler Sequencer:
http://www.syxthsense.com/ecommerce2/search.php?categoryID=4&subcategoryID=186
Weather compensator:
http://www.syxthsense.com/ecommerce2/cart1.php
Using the combis will be simple with no provision for DHW diverter valves or
the likes. The whole setup is very cheap and highly effective.
Ring Remeha, they may have an off-the-shelf solution incorporating integral
boiler weather compensation and boiler sequencing for their range.
Ed Sirett
This is something I've yet to do. I'm wondering how bad a really simple
approach would be.
Common both demands directly to both boilers and set one boiler to a
reasonable primary temperature (say 65-75C) and set the other boiler 1-3C
below the other. As the "lower" boiler reaches its target temp it will
fairly soon cut-out and (if poss) you can set it's anti-cycle time to a
longish value. It will only test the temperature every so often and if the
upper boiler is coping will again leave things alone.
I am not familiar enough with W-Bs to know if you can tweak the anti cycle
time. You can certinaly do this for Vaillants and Kestons.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Phil Addison
>This is something I've yet to do. I'm wondering how bad a really simple
>approach would be.
>
>Common both demands directly to both boilers and set one boiler to a
>reasonable primary temperature (say 65-75C) and set the other boiler 1-3C
>below the other. As the "lower" boiler reaches its target temp it will
>fairly soon cut-out and (if poss) you can set it's anti-cycle time to a
>longish value. It will only test the temperature every so often and if the
>upper boiler is coping will again leave things alone.
Thanks Ed, good point, so we could start off with no controls and have a
system that at least 'works'. Then experiment with added sophistication
later. That's an attractive proposition because we're keen to get
started with the colder weather imminent.
>I am not familiar enough with W-Bs to know if you can tweak the anti cycle
>time. You can certinaly do this for Vaillants and Kestons.
I'm disillusioned with W-B website and technical support, do you find
Vaillant and Keston satisfactory? I'll check out their data/prices.
I have a quote of £3860+vat for the whole job including 2x W-B 24i
system boilers, replacing flues to roof, condensate pump to gutter, and
wireless stat on a common landing. No controls offered - this firm
doesn't know anything about the subject. How does price that sound?
Phil
Phil Addison
<kill...@invalid.invalid> wrote:
>
>"Phil Addison" <phi...@bigNOSPAMfoot.com> wrote in message
>news:41k6i453g7lscslvf...@4ax.com...
>>
>> The proposal is that the two new boilers will each have their own pump
>> and check valve, and that combination will be connected in parallel and
>> tee'd into the existing low-loss header. A magnetic strainer will be
>> included.
>>
>> So far that seems straightforward. My concern is the control system to
>> ensure the pair of boilers work at maximum efficiency. When it is mild
>> we want one boiler only to be running, and the second cutting in only
>> when more that 24kW is required. Clearly one boiler running at full
>> power will be much more efficient than two running at half power. and
>> for most of the year we should see the benefit of full condensing
>> operation of one boiler with the other hardly ever firing.
>
>Buy a Broag Boiler (Dutch). They are top quality (better than Vaillant) and
>are now freely available...and cheaper too, as they are making headway into
>the UK market. Their boiler control systems are Opentherm and quite
>advanced. They are the best buy by far of any boiler at the mo'. They are
>well established in the UK under Remeha, doing excellent commercial stuff
>and decided to import their domestic Broag Avantaplus range.
>http://www.avantaplus.com/
Thanks, I'll check them out.
>I don't know what your DHW requirements are.
As mentioned, there is no DHW requirement.
>To do the sequencing of the two boilers try these below, which are cheap and
>OK. You will have to put the controls into a plastic control box.
>
>The 0-10v output of the weather compensator will input into the boiler
>sequencer, thus making one control unit. The boilers will be basic units
>with no external controls on them, only being controlled by the weather
>compensator via the sequencer.
>
>The weather compensator lowers the flow temperature of the boilers to
>promote condensing efficiency and the sequencer decides if one or two
>boilers needs to be brought in. Also, boiler cycling is at a minium.
>
>Boiler Sequencer:
>http://www.syxthsense.com/ecommerce2/search.php?categoryID=4&subcategoryID=186
Yes, this is interesting, I am awaiting some hopefully more meaningful
data than found on their site.
>Weather compensator:
>http://www.syxthsense.com/ecommerce2/cart1.php
Not sure that this sytem is value for money, will probably settle for
stat on combined return pipe. Or possibly a "0-10V modulating output"
from the boiler which I think is a measure of what the boiler thinks is
the required output power. I'm told W-B boilers have this but their site
is hopeless so difficult to check.
Anyone know any more about this output signal and if W-B does provide
it?
>Using the combis will be simple with no provision for DHW diverter valves or
>the likes. The whole setup is very cheap and highly effective.
See my reply to John Stumbles
>Ring Remeha, they may have an off-the-shelf solution incorporating integral
>boiler weather compensation and boiler sequencing for their range.
Anyone else heard of them?
Phil
Phil Addison
wrote:
>On Wed, 19 Nov 2008 00:25:12 +0000, Phil Addison wrote:
>
>> Thanks for the earlier advice on subject "Chaffoteaux FlexiFlame 140
>> boiler periodically cutting out". The decision has now been made to
>> replace it, and the recommendation we have, which I think is reasonable,
>> is to replace the ancient 41kW beastie with a pair of 24kW
>> Worcester-Bosch system boilers (model 24i) running in parallel.
>
>Not answering your question, I know, but my supplier charges more for the
>24i system boiler than the equivalent combi (24i Junior). So if you've got
>a use for instantaneous hot water (times two) from your setup you could
>have it effectively free.
Good tip. I don't need hot water, but if they are cheaper...
OTOH, presumably they are less reliable...
Phil
Phil Addison
<to...@delme.sda.co.uk> wrote:
>On Wed, 19 Nov 2008 08:38:29 +0000 David Hansen wrote :
>> As has been said you need a sequencer. Search engines will
>> pull up a whole variety from bare boards to finished products
>> in enclosures. One example of the former is
>> <http://www.intelligentheatingcontrol.co.uk/026.html>
>>
>> Such a gadget will allow you to set which boiler leads. That
>> can be done with a switch and thermostats, but an electronic
>> version allows for things like automatically changing which
>> boiler leads. It may offer other features like weather
>> compensation.
>
>If you read the tech sheet on this particular unit, the
>switching in or out of the second boiler is done by a pipe stat
>on the return as per my DIY system.
This one? http://www.warmworld.co.uk/sitedocs/sequencer_brochure.pdf
What a wierd site, went rouund it 3 times before I found that.
The second paragraph under Fuel Economy" saying about "the boiler will
oscillate on and off" worries me. That sounds like the instability I
mentioned in my initial post.
>The only refinement is that
>the lead boiler is automatically alternated every six hours -
>as already pointed out, taken to its logical conclusion this
>would lead to both boilers expiring together.
Seemingly done by a large analogue timeswitch bolted to the PCB!
I wonder how much they want for it; the syxthsence one is £94+vat,
though as yet I'm not at all sure exactly what it does.
Phil
Phil Addison
wrote:
>On Wed, 19 Nov 2008 08:38:29 +0000, David Hansen wrote:
>
>> Such a gadget will allow you to set which boiler leads. That can be
>> done with a switch and thermostats, but an electronic version allows
>> for things like automatically changing which boiler leads.
>
>Thought for the day: if you managed to even out the wear and tear between
>the boilers perfectly then you'd get the closest possible to them failing
>through wear and tear at the same time :-)
True, but at least it's some 2n years into the future rather than n.
Phil
Phil Addison
<SENDdavi...@spidacom.co.uk> wrote:
>On Wed, 19 Nov 2008 00:25:12 +0000 someone who may be Phil Addison
><phi...@bigNOSPAMfoot.com> wrote this:-
>
>>First question is, is there a standard 'box of tricks' that does this? I
>>have asked W-B who insist they "don't do system design just make
>>boilers" and could offer no help.
>
>As has been said you need a sequencer. Search engines will pull up a
>whole variety from bare boards to finished products in enclosures.
>One example of the former is
><http://www.intelligentheatingcontrol.co.uk/026.html>
>
>Such a gadget will allow you to set which boiler leads. That can be
>done with a switch and thermostats, but an electronic version allows
>for things like automatically changing which boiler leads. It may
>offer other features like weather compensation.
Thanks David, I am wading through google returns. These guys
http://www.syxthsense.co.uk/ are helpful on the phone, and I'm awaiting
some data from them.
Phil
Phil Addison
(Andrew Gabriel) wrote:
I don't follow this. You mean if the 2nd boiler fails (generates
lockout) you use this to fire up the lead boiler? But won't the lead
boiler be firing anyway?
>Of course, something like a
>failed mains supply won't generate lockout, but you could also
>generate your own lockout signal based on loss of supply. This
but with no mains neither would fire up whatever you do, unless you have
an aux supply?
>is exactly what I do with my system -- lockout, or failure of
>the boiler supply, triggers an input to my house alarm, which
>will then phone me up and tell me the boiler's failed. That still
>doesn't cover quite all failures modes. I've had the condensate
>trap block and the combustion chamber start filling with
>condensate. It still ran for a few hours with almost no heat
>output, before the condensate blocked off the flue outlet enough
>to go into lockout, and the alarm call me up.
Crikey, that's worrying, with our reliance on a condensate pump too. Any
ideas on failure detection in that area? The thought of the boiler
innards filling up with weak acid isn't too comforting.
>To be honest, the simplicity of your system would be hard to beat.
>As control systems get more complex, they normally get less
>relible and also more subject to design oversights, and it's not
>clear to me that any further gain you could make would be balanced
>by the inevitable risk of increased complexity.
That's a good point. However, as this system is over 4 floors I'm not
too happy with it being controlled by a room stat, which inevitably will
finish up in the common draughty stair way. I suspect this would just be
turned up high and the system then run on the TRVs. If this is the case
I don't see that TB's solution with a secondary room stat would work.
Phil
Phil Addison
<to...@delme.sda.co.uk> wrote:
>On Wed, 19 Nov 2008 00:25:12 +0000 Phil Addison wrote :
>> First question is, is there a standard 'box of tricks' that
>> does this? I have asked W-B who insist they "don't do system
>> design just make boilers" and could offer no help.
>
>The boxes that do this are called sequencers and don't come
>cheap.
Thanks Tony, "sequencer" is the magic word I was missing, got several
google hits now, http://www.syxthsense.co.uk/ loooks interesting.
>I had to do this when I replaced our church boiler with a pair of
>Kestons back in 2001 and needed a budget solution. What we ended
>up with is this:
>
>The ordinary controller goes into the common of a two-way switch
>(select lead boiler) with L1 and L2 going to the call for heat on
>each boiler. Between L1 and L2 there is a connection which goes
>through a room stat (a CM67 on our system) set 1/2 degree or so
>lower than the main one, and a pipe stat (normally closed, but
>set to open at about 60C) on the return from the heating.
By "ordinary controller" do you mean the main room stat? Is the
secondary room stst (your CM67) co-located with it?
>So from cold, both these stats are closed so L1 and L2 are
>connected and both boilers run. If the desired temperature is all
>but there, the second boiler drops out, and this also happens if
>the return temp reaches 60 (i.e the rads are not getting rid of
>the heat fast enough).
I like it, certainly seems to meet the basic requirements.
>I did try one or two other refinements but took them out so as
>not to make things too complicated for my successor.
I'm interested in what these were.
>One was to
>use an extra stat to delay pulling in the second one until the
>first boiler was fully up to temp (which it never gets to in the
>mild spring/autumn days), but without adding yet more
>complication this then means that if the first boiler fails, the
>second doesn't either,
>and one of the reasons for having a 2-boiler system is the backup.
Agreed re backup, plus these smaller domestic ones are readilly
available and may well be cheaper than a single biggie.
>In terms of a simple solution, what I really needed (Andrew could
>no doubt have designed something), was a delay controller that
>would close a relay (say) 15 minutes after power was supplied, so
>that in spring/autumn when the boiler was being cycled it never
>closed, and if the lead boiler failed the second one was pulled
>in after a short delay.
Sounds like a re-triggerable delay; the delay is restarted everytime it
gets a trigger signal so it won't timeout till a "delay time" after
triggering stops. Very easy to implement based on a 555 IC.
On a slightly different point, the installer is proposing to pump the
condensate up through the cieling and out into the gutter, the boiler
being on the top floor of a 4-story building and no easy route to a
drain. I can't see any real objection, but is this ok?
Phil
Doctor Drivel
"Phil Addison" <phi...@bigNOSPAMfoot.com> wrote in message
Try this:
http://www.syxthsense.com/ecommerce2/product_pdf/MOD3.46-BPRO4A.pdf
>>Weather compensator:
>>http://www.syxthsense.com/ecommerce2/cart1.php
>
> Not sure that this sytem is value for money, will probably settle for
> stat on combined return pipe.
You need weather compensation and a sequence controller.
> Or possibly a "0-10V modulating output"
> from the boiler which I think is a measure of what the boiler thinks is
> the required output power. I'm told W-B boilers have this but their site
> is hopeless so difficult to check.
0-10v output? Do you mean input? 0-10v is in commercial systems. I know
of no domestic boiler that has a 0-10v input. I think MAN "may" have this.
No integrated weather compensation/sequencing controller in the OpenTherm
protocol.....yet. Once they do it will shine.
Phil Addison
<kill...@invalid.invalid> wrote:
>
>Buy a Broag Boiler (Dutch). They are top quality (better than Vaillant) and
>are now freely available...and cheaper too, as they are making headway into
>the UK market. Their boiler control systems are Opentherm and quite
>advanced. They are the best buy by far of any boiler at the mo'. They are
>well established in the UK under Remeha, doing excellent commercial stuff
>and decided to import their domestic Broag Avantaplus range.
>http://www.avantaplus.com/
Avanta Plus 24s looks promising, 2x £564+vat (£1128) from
www.tradingdepot.co.uk, and I can't see any obvious snags on their
website - except I never heard of them before, but got nothing against
dutch kit in principle. It does seem to have all the bells and whistles.
This compares to 2x £652 (£1304) for the Worcester-Bosch 24i from my
local PlumbCentre.
Vailent ecoTEC plus 624 looks very expensive.
But then I found a Glow-worm 18HX £ 480 plus a 24HX at £499 (£979) also
at www.tradingdepot.co.uk - and this is a better match to the existing
41kw chaffateaux, although it does not give quite equal redundancy, 44%
vs 56% worst case failed output compared to the 41kw assumed
requirement.
Any opinions?
Phil Addison
<kill...@invalid.invalid> wrote:
Already read that, its appallingly written and doesn't really explain
anything.
>>>Weather compensator:
>>>http://www.syxthsense.com/ecommerce2/cart1.php
>>
>> Not sure that this sytem is value for money, will probably settle for
>> stat on combined return pipe.
>
>You need weather compensation and a sequence controller.
I don't consider weather comp necessary at all, and as per my response
to Ed, it does seem possible to work with no sequencer at all, though
may not be ideal.
>> Or possibly a "0-10V modulating output"
>> from the boiler which I think is a measure of what the boiler thinks is
>> the required output power. I'm told W-B boilers have this but their site
>> is hopeless so difficult to check.
>
>0-10v output? Do you mean input? 0-10v is in commercial systems. I know
>of no domestic boiler that has a 0-10v input. I think MAN "may" have this.
I do mean output (from each boiler) which when fed into a sequencer will
decide whether to switch the other boiler on. Your syxthsense man says
he thinks WB have that, I havent asked WB themselves as yet, and as said
the data on their site is pathetic.
The alternative it to measure common return temp in the LLH.
>No integrated weather compensation/sequencing controller in the OpenTherm
>protocol.....yet. Once they do it will shine.
Bit of an overkill for 2 boilers dont you think?
Tony Bryer
> Common both demands directly to both boilers and set one boiler
> to a reasonable primary temperature (say 65-75C) and set the
> other boiler 1-3C below the other. As the "lower" boiler reaches
> its target temp it will fairly soon cut-out and (if poss) you can
> set it's anti-cycle time to a longish value. It will only test
> the temperature every so often and if the upper boiler is coping
> will again leave things alone.
My impression (perhaps wrong) with our Kestons was that this
strategy doesn't work very well as the boiler just modulates down
as the set temperature is reached - you're more likely to see two
boilers running with 1 or 2 lights (of 4) running
Tony Bryer
> By "ordinary controller" do you mean the main room stat? Is
> the secondary room stst (your CM67) co-located with it?
Ideally they would be, but the main CM67 is a wireless one on
a side wall - has been moved several times to find an optimum
position, whilst the second boiler one is a wired one where
the original stat was. The override one is programmed on a
rough and ready basis.
> >So from cold, both these stats are closed so L1 and L2 are
> >connected and both boilers run. If the desired temperature
is
> >all but there, the second boiler drops out, and this also
> >happens if the return temp reaches 60 (i.e the rads are not
> >getting rid of the heat fast enough).
>
> I like it, certainly seems to meet the basic requirements.
>
> >I did try one or two other refinements but took them out so
> >as not to make things too complicated for my successor.
>
> I'm interested in what these were.
One was an extra pipe stat on the low-loss header that kept
the second boiler off until the first was hot, abandoned
because a failure of the first meant the second never fired,
and one was an extra room stat in an unheated area that kept
the second boiler running on the coldest days regardless of
inside temp (which in practice on such days would struggle to
get to the desired).
Tony Bryer
> 0-10v output? Do you mean input? 0-10v is in commercial systems.
> I know of no domestic boiler that has a 0-10v input. I think MAN
> "may" have this.
No, but on the www.syxthsense.com site there is a sequencer that will
switch one or both boilers depending on the applied voltage.
Doctor Drivel
"Phil Addison" <phi...@bigNOSPAMfoot.com> wrote in message
>>Try this:
>>http://www.syxthsense.com/ecommerce2/product_pdf/MOD3.46-BPRO4A.pdf
>
> Already read that, its appallingly written
> and doesn't really explain anything.
You are obviously not technical enough to understand it.
>>>>Weather compensator:
>>>>http://www.syxthsense.com/ecommerce2/cart1.php
>>>
>>> Not sure that this sytem is value for money, will probably settle for
>>> stat on combined return pipe.
>>
>>You need weather compensation and a sequence controller.
>
> I don't consider weather comp necessary
> at all, and as per my response
> to Ed, it does seem possible to work with
> no sequencer at all, though
> may not be ideal.
If you want a highly efficient system running at maximum economy then
weather compensation you do need, especially when burning so much gas as you
will be. I don't think you understand what it does and what it gives. It
will not cost much to do. It keeps the flow temperature as low as possible
promoting maximum condensing efficiency. You don't fit two condensing
boiler and try to sequence them using simple stats.
What do you want? A simple boiler sequencer? Then just fit the Warmworld
model and keep the boilers on maximum temperature. You will then only be
doing half the control setup, leaving out weather compensation.
I think the best thing for you is to drop the two boilers idea and fit one
boiler with integral weather compensation, as I doubt you will control the
two of them properly or efficiently.
I have seen so many systems working inefficiently because of poor control.
>> 0-10v output? Do you mean input? 0-10v
>> is in commercial systems. I know of no domestic
>> boiler that has a 0-10v input. I think MAN "may"
>> have this.
>
> I do mean output (from each boiler) which
> when fed into a sequencer will
> decide whether to switch the other boiler on.
> Your syxthsense man says
> he thinks WB have that, I havent asked WB
> themselves as yet, and as said
> the data on their site is pathetic.
Sequencers do not work that way. They control "both" boilers and it decides
when to switch them in. On cold start, both boilers will be on full. As the
setpoint temperature nears, the lag boiler will be switched out, then the
remaining boiler will modulate on itself until setpoint is reached and then
the sequencer switches that out. On commercial systems, each stage will
modulate the burner of each boiler, so both on full, the lag boiler
modulates down, then off, the lead boiler modulates down until off.
I think what you are after is a boiler that says I am on full and gives a
signal saying so which switches in the lag boiler. When on less than full
burner rate the lag boiler is switched out as it is not needed. This is
simple and simple for the makers to put into a pcb, and would eliminate a
sequence controller. I know of no open who does it. If you find one let us
know.
> The alternative it to measure common return temp in the LLH.
>
>>No integrated weather compensation/sequencing
>>controller in the OpenTherm
>>protocol.....yet. Once they do it will shine.
>
> Bit of an overkill for 2 boilers dont you think?
No. As I understand control.
I am not aware that any OpenTherm protocol boiler accepts a 0-10v signal
that modulates the burner. If so, the two controllers I gave, would be
ideal. The weather compensator gives a 0-10v output signal into the
sequencer, which in turn outputs 0-10v into each boiler which uses the
signal to modulate the burner.
I'll look further if I have time.
Doctor Drivel
"Tony Bryer" <to...@delme.sda.co.uk> wrote in message
news:VA.0000471...@delme.sda.co.uk...
> On Thu, 20 Nov 2008 01:26:50 -0000 Doctor Drivel wrote :
>
>> 0-10v output? Do you mean input? 0-10v is in commercial systems.
>> I know of no domestic boiler that has a 0-10v input. I think MAN
>> "may" have this.
>
> No, but on the www.syxthsense.com site there is a sequencer that will
> switch one or both boilers depending on the applied voltage.
I know that. He is on about a boiler "outputting" a 0-10v signal. He is
confused a little.
Doctor Drivel
"Phil Addison" <phi...@bigNOSPAMfoot.com> wrote in message
The Broag is a quality model with a far superior OpenTherm control system -
the Dutch invnetd the condensing boiler and most quality models are Dutch,
like Atmos. It has: Gianonni heat exchanger, Grundfos pump, Dung gas valve,
etc.
The Glow Worm HX is a open vented heating boiler (no pump) The SX is the
system boiler. The Flexicom range I think are cast off Vaillant models. The
better GlowWorm range is the Ultracom.
Doctor Drivel
"Doctor Drivel" <kill...@invalid.invalid> wrote in message
news:gg3i24$tbq$1...@news.motzarella.org...
> I think the best thing for you is to drop the two boilers idea and fit one
> boiler with integral weather compensation, as I doubt you will control the
> two of them properly or efficiently.
Look at a the Broag Avantapluc 39C combi. A few kW below your old boiler - a
good match. You then don't need to connect the water section and just use
the CH side. It is well priced and has the weather compensation control. It
is £917 inc VAT, that is very well priced for a 40kW boiler. If you need
the water part in the future you have it. Or connect it up and isolate the
DHW section and use as backup only.
http://www.tradingdepot.co.uk/DEF/catalogue/D003001007/Plumbing/Central%20Heating/Central%20Heating%20Boilers/Broag%20Remeha%20Boilers
Look at the combi options pages 17 to 21. The outside senors etc, are extra.
http://www.avantaplus.com/docs/Issue%205%20-Avanta%20Schematics%20Booklet.pdf
The Broag 28kW combi costs less than the 24kW system boiler, because of
bigger sales, competition, etc. A combi is a system boiler with a water
section. You do not need to use the water section.
Tony Bryer
> If you want a highly efficient system running at maximum economy then
> weather compensation you do need, especially when burning so much gas
> as you will be. I don't think you understand what it does and what it
> gives. It will not cost much to do. It keeps the flow temperature as
> low as possible promoting maximum condensing efficiency. You don't fit
> two condensing boiler and try to sequence them using simple stats.
It's the return temp that you need to keep down, and a stat on the
heating return achieves just that. BRE reckon that weather compensation
will improve a gas system's efficiency by 2%, but of course this is only
2% of the heating (not DHW) cost, so on smaller or well insulated
properties it is not cost effective.
Doctor Drivel
> On Thu, 20 Nov 2008 11:23:20 -0000 Doctor Drivel wrote :
>> If you want a highly efficient system running at maximum economy then
>> weather compensation you do need, especially when burning so much gas
>> as you will be. I don't think you understand what it does and what it
>> gives. It will not cost much to do. It keeps the flow temperature as
>> low as possible promoting maximum condensing efficiency. You don't fit
>> two condensing boiler and try to sequence them using simple stats.
>
> It's the return temp that you need to keep down, and a stat on the
> heating return achieves just that.
But not very well or efficiently and it will use more gas.
> BRE reckon that weather compensation
> will improve a gas system's efficiency by 2%, but of course this is only
> 2% of the heating (not DHW) cost, so on smaller or well insulated
> properties it is not cost effective.
As many boilers come with weather compensation as standard it is highly cost
effective indeed. Even a BIASI model has integral compensation. Danfoss
and Honeywell have dropped their stand alone weather compensators as they do
not sell enough as integral compensators have stolen their market.
BRE tests. Where they using OpenTherm control types where the burner
modulates to the demand? I doubt it. In this case where 40kW is being
burned it makes lots of sense.
Also, weather compensation improved comfort levels too.
Doctor Drivel
"Phil Addison" <phi...@bigNOSPAMfoot.com> wrote in message
>>Kestons very handily (and as far as I know, uniquely in domestic
>>boiler sizes) have a lockout output signal, so providing the failure
>>is of a type which generates a lockout, you could use this to
>>effectively switch the lead boiler.
>
> I don't follow this. You mean if the 2nd boiler fails (generates
> lockout) you use this to fire up the lead boiler? But won't the lead
> boiler be firing anyway?
What he is referring to is a backup boiler rather than a lag boiler. If a
boiler locks out it brings in backup. Different to lead-lag boiler
sequencing.
>>To be honest, the simplicity of your system would be hard to beat.
>>As control systems get more complex, they normally get less
>>relible and also more subject to design oversights, and it's not
>>clear to me that any further gain you could make would be balanced
>>by the inevitable risk of increased complexity.
Quality modern boilers with integral weather compensation are very reliable
and not complex in controls terms. All this came from the commercial sector
which has had this for many decades. Well proven.
Doctor Drivel
cheaper and bigger kW, and don't use the water sections. Use the integral
weather compensation for both (two outside sensors). Just adjust the
compensation control slope on each boiler so one boiler is always lagging
the other. Setting up the compensation slope is easy on the Broag
Avantaplus. That is a very cost effective way of getting what you want.
YAPH
> Good tip. I don't need hot water, but if they are cheaper...
> OTOH, presumably they are less reliable...
Presumably, yes, though - like most current generation combis - they use a
hall-effect turbine to sense DHW flow, rather than a diverter valve with
a diaphragm that's prone to splitting. But even allowing for them being
less reliable in total, including the DHW function, the space-heating
function should be no less reliable. And if you have (and keep) a
conventional DHW system as well the total set-up should be /more/ reliable
by giving you 3 separate sources of DHW!
--
John Stumbles -- http://yaph.co.uk
I'd give my right arm to be ambidextrous
YAPH
> Anyone else heard of them?
I've heard of them (Remeha), but not heard much. One of the guys on my
recent ACS reassessment seemed quite keen on them, and he seemed a clueful
sort of person. I know he put one in on a job I passed to him because I
couldn't fit it in, but of course it's only been running a few weeks.
Another thing I heard about them (though from a general builder with FA^-2
heating knowledge :-)) was that they had (past tense, at least) had a poor
reputation for reliability.
Funnily enough their premises are across the road from the gas training
centre we did our ACses at, in Wokingham.
--
John Stumbles -- http://yaph.co.uk
I'm more non-competitive than you
Doctor Drivel
"YAPH" <use...@yaph.co.uk> wrote in message
news:kglVk.136717$QH3....@newsfe16.ams2...
> On Wed, 19 Nov 2008 19:59:38 +0000, Phil Addison wrote:
>
>> Good tip. I don't need hot water, but if they are cheaper...
>> OTOH, presumably they are less reliable...
>
> Presumably, yes, though - like most current generation combis - they use a
> hall-effect turbine to sense DHW flow, rather than a diverter valve with
> a diaphragm that's prone to splitting.
Few combis have pressure operated diaphragms. They are mostly electric 3-way
valves.
> But even allowing for them being
> less reliable in total, including the DHW function,
They are not overall. If a mid-position 3-way valve ma;functions on a
cylinder one blames the bonier. It is reliability of system vs. system.
YAPH
> This compares to 2x £652 (£1304) for the Worcester-Bosch 24i from my
> local PlumbCentre.
£584 + VAT (for the 24i Junior combi) from PlumbNation - who actually buy
and get deliveries through PlumbCentre, so if you talk to the manager at
your PlumbCentre and show him the PlumbNation prices he should be able to
match or beat them.
--
John Stumbles -- http://yaph.co.uk
What do you mean, talking about it isn't oral sex?
Doctor Drivel
> On Wed, 19 Nov 2008 19:59:28 +0000, Phil Addison wrote:
>
>> Anyone else heard of them?
>
> I've heard of them (Remeha), but not heard much. One of the guys on my
> recent ACS reassessment seemed quite keen on them, and he seemed a clueful
> sort of person. I know he put one in on a job I passed to him because I
> couldn't fit it in, but of course it's only been running a few weeks.
>
> Another thing I heard about them (though from a general builder with FA^-2
> heating knowledge :-)) was that they had (past tense, at least) had a poor
> reputation for reliability.
That is totally 180 degrees to the common view of Broag.
YAPH
> The Broag is a quality model with a far superior OpenTherm control
> system - the Dutch invnetd the condensing boiler and most quality models
> are Dutch, like Atmos. It has: Gianonni heat exchanger
Gas News had an interesting article about this HX, in which they raised
some questions about its potential reliability:
http://www.gas-news.co.uk/archive/storage/pre-10/2007/comment/1006.htm
--
John Stumbles -- http://yaph.co.uk
I used to be forgetful but now I ... um ....
Doctor Drivel
> On Thu, 20 Nov 2008 11:34:58 +0000, Doctor Drivel wrote:
>
>> The Broag is a quality model with a far superior OpenTherm control
>> system - the Dutch invnetd the condensing boiler and most quality models
>> are Dutch, like Atmos. It has: Gianonni heat exchanger
>
> Gas News had an interesting article about this HX, in which they raised
> some questions about its potential reliability:
> http://www.gas-news.co.uk/archive/storage/pre-10/2007/comment/1006.htm
Fit a Maganclean and solids do not enter the heat exchanger.
Gianonni supply heat exchangers to many top rated makers.
Ed Sirett
>
>>is exactly what I do with my system -- lockout, or failure of the boiler
>>supply, triggers an input to my house alarm, which will then phone me up
>>and tell me the boiler's failed. That still doesn't cover quite all
>>failures modes. I've had the condensate trap block and the combustion
>>chamber start filling with condensate. It still ran for a few hours with
>>almost no heat output, before the condensate blocked off the flue outlet
>>enough to go into lockout, and the alarm call me up.
>
> Crikey, that's worrying, with our reliance on a condensate pump too. Any
> ideas on failure detection in that area? The thought of the boiler
> innards filling up with weak acid isn't too comforting.
A typical condensate pump will have an 'alarm' float switch (The
Sanicondens has a changecover switch) this can be used to stop the boiler
and/or show a fault light or sounds an alarm.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Ed Sirett
> On Wed, 19 Nov 2008 18:15:41 GMT Ed Sirett wrote :
>> Common both demands directly to both boilers and set one boiler to a
>> reasonable primary temperature (say 65-75C) and set the other boiler
>> 1-3C below the other. As the "lower" boiler reaches its target temp it
>> will fairly soon cut-out and (if poss) you can set it's anti-cycle time
>> to a longish value. It will only test the temperature every so often
>> and if the upper boiler is coping will again leave things alone.
>
> My impression (perhaps wrong) with our Kestons was that this strategy
> doesn't work very well as the boiler just modulates down as the set
> temperature is reached - you're more likely to see two boilers running
> with 1 or 2 lights (of 4) running
I'd try a slightly bigger 'split' between the two units in this case.
Ed Sirett
> On Wed, 19 Nov 2008 18:15:41 GMT, in uk.d-i-y Ed Sirett
> <e...@makewrite.demon.co.uk> wrote:
>
>>On Wed, 19 Nov 2008 00:25:12 +0000, Phil Addison wrote:
>>
>>> Thanks for the earlier advice on subject "Chaffoteaux FlexiFlame 140
>>> boiler periodically cutting out". The decision has now been made to
>>> replace it, and the recommendation we have, which I think is
>>> reasonable, is to replace the ancient 41kW beastie with a pair of
>>> 24kW Worcester-Bosch system boilers (model 24i) running in parallel.
>>>
>>> This existing system is sealed, and the Chaffoteaux has an internal
>>> pump circulating primary water through a low-loss header* (LLH), and
>>> there is a separate pump circulating the LLH contents around the
>>> radiators which are spread over 4 floors, see ASCII art below. This is
>>> heating only, no domestic hot water.
>>>
>>> Currently one radiator is open valved and the others have TRVs.
>>>
>>> The proposal is that the two new boilers will each have their own pump
>>> and check valve, and that combination will be connected in parallel
>>> and tee'd into the existing low-loss header. A magnetic strainer will
>>> be included.
>>>
>>> So far that seems straightforward. My concern is the control system to
>>> ensure the pair of boilers work at maximum efficiency. When it is mild
>>> we want one boiler only to be running, and the second cutting in only
>>> when more that 24kW is required. Clearly one boiler running at full
>>> power will be much more efficient than two running at half power. and
>>> for most of the year we should see the benefit of full condensing
>>> operation of one boiler with the other hardly ever firing.
>>
>>
>>This is something I've yet to do. I'm wondering how bad a really simple
>>approach would be.
>>
>>Common both demands directly to both boilers and set one boiler to a
>>reasonable primary temperature (say 65-75C) and set the other boiler
>>1-3C below the other. As the "lower" boiler reaches its target temp it
>>will fairly soon cut-out and (if poss) you can set it's anti-cycle time
>>to a longish value. It will only test the temperature every so often and
>>if the upper boiler is coping will again leave things alone.
>
> Thanks Ed, good point, so we could start off with no controls and have a
> system that at least 'works'. Then experiment with added sophistication
> later. That's an attractive proposition because we're keen to get
> started with the colder weather imminent.
>
>>I am not familiar enough with W-Bs to know if you can tweak the anti
>>cycle time. You can certinaly do this for Vaillants and Kestons.
>
> I'm disillusioned with W-B website and technical support, do you find
> Vaillant and Keston satisfactory? I'll check out their data/prices.
>
If the current system use a sealed primary and you wanted to install 2
x20kW and the flue was straight forward I'd go for the Vaillant. What's
more they might have the controls as a package.
Check the price of the 20kW system boiler against the 24kW combi (19kW max
for heating).
I think the Kestons would be 2x 28kW (do they do smaller?).
If the flue is awkward this is the way anyway.
If you are making your own control system, or if the primary is open
vented then the W-B is the choice.
> I have a quote of £3860+vat for the whole job including 2x W-B 24i
> system boilers, replacing flues to roof, condensate pump to gutter, and
> wireless stat on a common landing. No controls offered - this firm
> doesn't know anything about the subject. How does price that sound?
>
Any one who does this job must (Building regs) add TRVs to the system.
This job is slightly less work than doing do complete systems (but not by
much).
Ed Sirett
Have you use one of the web calculators to get another estimate of the
actuall heating requirement? If it came out loads less than 41kW it would
make me do some more investigations.
What was the duty cycle of the 41kW previous unit?
dennis@home
"Ed Sirett" <e...@makewrite.demon.co.uk> wrote in message
news:rkmVk.1885$qu1...@newsfe25.ams2...
> Any one who does this job must (Building regs) add TRVs to the system.
> This job is slightly less work than doing do complete systems (but not by
> much).
ITYM must fit proper controls of which TRVs are the worst option you can get
away with.
dennis@home
"Ed Sirett" <e...@makewrite.demon.co.uk> wrote in message
news:pomVk.1976$qu1....@newsfe25.ams2...
> Have you use one of the web calculators to get another estimate of the
> actuall heating requirement? If it came out loads less than 41kW it would
> make me do some more investigations.
>
> What was the duty cycle of the 41kW previous unit?
I think he would be better off spending half the cash on some sort of heat
recovery and insulation and fitting one boiler.
You can fit a filtered air unit with heat exchanger for the sort of money a
second boiler and controls cost.
That with CWI and loft insulation should reduce the heat loss by a lot.
Doctor Drivel
"dennis@home" <den...@killspam.kicks-ass.net> wrote in message
news:gg5t69$f8b$1...@news.datemas.de...
>
>
> "Ed Sirett" <e...@makewrite.demon.co.uk> wrote in message
> news:pomVk.1976$qu1....@newsfe25.ams2...
>
>> Have you use one of the web calculators to get another estimate of the
>> actuall heating requirement? If it came out loads less than 41kW it would
>> make me do some more investigations.
>>
>> What was the duty cycle of the 41kW previous unit?
>
> I think he would be better off spending half the cash on some sort of heat
> recovery and insulation and fitting one boiler.
The cost of two cheap 24kW boilers can be cheaper than one 45kW boiler, or
not much in it.
He should fit more insulation and then do recalc on heat loss.
Doctor Drivel
> On Wed, 19 Nov 2008 19:59:28 +0000, Phil Addison wrote:
>
>> Anyone else heard of them?
>
> I've heard of them (Remeha), but not heard much. One of the guys on my
> recent ACS reassessment seemed quite keen on them, and he seemed a clueful
> sort of person. I know he put one in on a job I passed to him because I
> couldn't fit it in, but of course it's only been running a few weeks.
>
> Another thing I heard about them (though from a general builder with FA^-2
> heating knowledge :-)) was that they had (past tense, at least) had a poor
> reputation for reliability.
BTW, they have a 5 year guarantee.
Ed Sirett
That's not what I meant. TRVs are _part_ of the control system along with
timers and thermostats and maybe other stuff.
John Stumbles
> Gianonni supply heat exchangers to many top rated makers.
And to Pox^H^H^HBaxi-Potterton :-)
--
John Stumbles
Fundamentalist agnostic
Doctor Drivel
"John Stumbles" <john.s...@ntlworld.com> wrote in message
news:s2IVk.91110$E41....@text.news.virginmedia.com...
> On Thu, 20 Nov 2008 22:54:50 +0000, Doctor Drivel wrote:
>
>> Gianonni supply heat exchangers to many top rated makers.
>
> And to Pox^H^H^HBaxi-Potterton :-)
Who slap it together poorly.
Phil Addison
Thanks for all the advice. However, it now looks as if the problem of
controlling 2 boilers is going away, because a re-assement of the
required heat output is looking as if the existing boiler is well
over-sized. A first estimate from the existing rad sizes indicates in
region of 23kw is required. I don't know the exact output of the rads so
think a single 24kw WB is marginal, and two of them totally too much,
but there is now a 30 and 40 kw WB available. It seems likely a single
WB 30CDi Conventional will be a good choice subject to doing a more
accurate heat-loss calc, and its not particularly expensive, certainly
less than 2 smaller ones.
Just for info, the biggest problem now is access to the roof to fit the
flue, being 4 storeys up, and we are looking at putting a Velux in the
loft to give access from inside.
Thanks again for the input, hope the discussion of 2-boiler controls
proved interesting to others, it certainly was for me. It seems an area
where acceptable control laws are not readily available or clearly
defined. My Google search wasn't very productive, the best I found was
the www.syxthsense.com site but even that only describes its controller
in marketing-speak.
Phil